Apparatus for automatically reducing the stroke of a free piston engine during low load conditions of an associated receiver machine



3,016,689 E OF Jam 1962 R J. BAYER ETAL APPARATUS FOR AUTOMATICALLYREDUCING THE STROK A FREE PISTON ENGINE DURING LOW LOAD CONDITIONS OF ANASSOCIATED RECEIVER MACHINE Filed Feb. 15, 1960 \R INVENTORS frobenefiia er 7222 H my ATTORNEY Bfilbfib Patented Jan. 16, 1962 AR ARA USAUTGMATHCALLY REDUSHN'G THE STufiKE A ihiSTilN ENGiNE EUR 1 Al)CGNDETEGN AN AS30- lni'lc i l/KER MACHINE .i. ayer, Warren, Raymond M.Cole, Royal Gal-r, and George ll. Stoughton, Rochester, l /lich. ast-ignore to General Motors Qorporation, li e-trot their, a corporationof Delaware Feb. 15, 1%). Ser. No. 8,322 2 Claims. (El. 6ll l3) Thisinvention relates to free piston engines and, more particula'ly, to ameans for improving the efiicieucy of such engines at low load or idlecondition.

The invention is shown as applied to a free piston diesel cycle gasifierwhich supplies combustion gases under pressure to drive a turbine orother suitable receiver machine. it is known that the delivery from agasifier can be regulated as to pressure and quantity to therequiremerits of the receiver machine over the ordinary load rangethereof by regulating the amount of fuel which is supplied to thegasifier combustion chamber. It is also known that the minimum deliveryof the gasifier is determined by the compression ignition point and thatthis minimum delivery will exceed the capacity of the receiver machinewhen the diesel intake and exhaust ports are arranged to provide goodeificiency under medium and full load conditions. Because of this it hasbeen common practice to feed only a portion of the gasifiers exhaust tothe receiver machine at low load and idle and to allow the remainder toblow off to atmosphere With a consequent loss of eificiency.

The object of this invention is to reduce and even obviate the surplusdelivery of the gasifier that occurs with light loading or idle runningof the receiver machine.

The delivery of the gasifier is reduced at low load and idle conditionsby incorporating an auxiliary set of intake and exhaust ports in thediesel cylinder between the main intake and exhaust ports and to openthe auxiliary ports under such low load and idle conditions. The minimumstroke of the gasifier can thus be shortened at such conditions as itneed only be long enough to uncover the auxiliary ports and thecompression ignition point can be maintained without affecting thelonger strokes which will occur at normal or full loads when theauxiliary ports are closed. The reduction in stroke at low gasifierexhaust pressures reduces the delivery to the receiver machine and thusobviates the need to blow off gasifier exhaust at light loads. To obtainefficient operation of the gasiiier at higher loads, it is necessarythat the auxiliary ports be closed; otherwise, the expansion ratio andstroke would be reduced when they should be increased.

In the drawings:

IGURE 1 is a diagrammatic longitudinal section of a free piston gasifierin accordance with the invention and shown as feeding a turbine toproduce shaft power.

FIGURE 2 is a partial section of the gasifier taken along the planeindicated by the line 2-2 of FIGURE 1 and illustrating the auxiliaryexhaust ports in light load position, and

FIGURE 3 is a partial section similar to FIGURE 2 and illustrating theauxiliary exhaust ports in heavy load position.

Referring to the drawings the gasifier iii operates on the two strokediesel principle and comprises a central diesel cylr ler ll having maininlet ports 12 and main exhaust ports 13 with a pair of opposed dieselpistons 14 and 15 serving to uncover such ports in the conventionalmanner as the pistons approach their outer dead points. The inner andouter dead points of the pistons 14 and 15 are variable in accordancewith various operating conditions.

The diesel cylinder 11 also has a fuel injector 16 centrally disposedtherein and connected by conduit 17 to an injection pump 18.

The diesel pistons 14 and 15 have compressor pistons 19 and 2d securedthereto which operate in compressor cylinders 21 and 22 to form cushionchambers 23 and 24 and compressor chambers and 26. The compressorchambers 25 and 26 have intake valves 27 and 28 through which the air tobe compressed is drawn and delivery valves 29 and 3!) which are fittedin separating walls 31 and 32 to deliver compressed air to anaccumulator or scavenge chamber 33 which is formed by the walls, thediesel cylinder ll and an engine case 34. The compressed air in thescavenge chamber 33 serves to supply and scavenge the diesel cylindercombustion chamber 35 through the intake ports 12 in the usual mannerunder heavy load conditions.

The cushion chambers 23 and 2 store the energy of the free pistonsduring their outward strokes under the influence of the combustion ofthe fuel in the diesel cylinder ii and return the energy to the pistonsfor the inward strokes th reef which effect compression in thecompressor chambers 25' and 26, delivery of compressed air to thescavenge chamber 33 and the compression of the diesel cylindercombustion air in the combustion chamber 35 after the pistons haveclosed the ports 12 and 13.

The injection pump 18 has a pump plunger 36 which is operated from alever 37 secured to one of the synchronizing rods 33 and 3's of the freepiston assemblies. The synchronizing rods 33 and 39 are fixed to thecompressor pistons 19 and 20 and have a rack and pinion connection witheach other at to maintain the piston assemblies in synchronization. Thelever 37 operates the pump 18 as the pistons approach their inner deadpoints to cause fuel injection and the quantity of fuel injected isregulated in the conventional manner by a rack 41 which causes thepiston of the pump to rotate about its axis. The quantity or" fuelinjected per cycle of piston movement is greater as the rack 4i is moveddownwardly in the drawing.

The movements of the rack 41 are effected automati cally in dependenceupon the load demand. of the receiver machine which comprises a gasturbine 42, the inlet of which is connected by a pipe 43 to an exhaustcollector that receives the diesel cylinder discharge by way of theexhaust ports 13 as the pistons approach their outer dead point. inorder to obtain automatic control of the rack ll, a governor 4-5 isprovided to variably pressurize a liquid in a pipe 4% which connects toa cylinder 47 to operate a piston 4% against a spring a9 and move a bellcrank 51 about its pivot 5i. through push rod 52, the bell crank 59being connected to the rack 41 by a link 53. The governor is so arrangedthat with an increase in load on the turbine the pressure in the conduit46 will increase and the rack ll. will. be moved increasingly down wardto increase the amount of fuel injected.

The amount or" fuel injected into the gasiiier is held within maximumand minimum limits which are variable in dependence on the workingpressure of the gasifier, i.e., the pressure in the scavenge chamber 33or exhaust conduit 4-3, and the rack 41', accordingly has its movementsregulated Within such limits by cams 5'4 and 55 which are formed on thebell crank to engage a movable stop 56 and to the limits. The stop 55 iscarried by a piston 57' which engages a spring 58 in a cylinder 59. Aconduit so places the cylinder 55' in communication with the scavengechamber 33 so that one face of the piston 57 is acted upon by thepressure in the scavenge air chamber in opposition to the spring 5 3.The position of the movable stop as thus varies in dependence upon theworking pressure of the gasiiier and the engagement of the stop with thecam 5 thus sets the minimum values of fuel injection in dependence onworking pressure and the maximum values of fuel injection are likewisethus set by the engagement of the stop with the cam 55. During normaloperation the stop 56 does not engage the cams 54- or 55 and theposition of the fuel rack 41 is directly dependent on the controlpressure from the governor 45.

The cushion chambers 23 and 2d are connected by conduits 61 and 62 sothat their pressure fluctuations will be in balance and are alsoconnected to a conventional stabilizer 63 which has conduit connections64 and 65 to the scavenge air chamber 33. The stabilizer controls themass of air in the cushion chambers in dependence on the gasifiersworking pressure which is variable in accordance with the load. Thestabilizer 63 consists of a slide valve 66 formed into two internalchambers 67 and 68 which communicate with each other by a check valve69. The slide valve 66 reciprocates in a valve chest 70 so that thechambers 67 or 68 can communicate with the valve chest chamber 71 by wayof apertures 72 or 73. The valve chest chamber 71 is connected to theworking pressure of the engine case by way of the conduit 6 Thestabilizer 63 forms a compartment 74 about the valve 66 and valve chest70 and this compartment is supplied with cushion chamber pressure by theconduit 61. When the slide valve 66 is moved to the left, air can flowfrom the cushion chambers to the scavenge air box by way of the conduit61, chamber 74, aperture 73, check valve 69, aperture 72, chamber 71 andconduit 64 as long as the cushion chamber pressure exceeds the scavengepressure. When the slide valve 66 is moved to the right, air can flowfrom the scavenge air chamber to the cushion chamber by way of theconduit 64, chamber 71, aperture 73, check valve 69, aperture 72,chamber 74 and conduit 61 as long as the scavenge air pressure exceedsthe cushion chamber pressure.

The scavenge air chamber pressure remains fairly uniform at any givenload and rises with load increases. The cushion chamber pressure variesin accordance with the position of the piston assemblies and drops belowthe scavenge pressure when the assemblies approach inner dead point andrises above scavenge pressure when they approach outer dead point. It isthus possible to vary the mean pressure of the cushion chambers inaccordance with the working pressure of the gasifier by transferring airbetween the scavenge air chamber and cushion cham her through thestabilizer. The slide valve 66 is shifted to accomplish this airtransfer by a stepped piston 75 which is disposed inside a cylinder 76.A restrictor orifice 77 provides a means for supplying the mean pressureof the cushion chambers to the larger face of the stepped piston 75 inopposition to the working pressure of the gasifier which is supplied tothe smaller face by the conduit 65. The dimensioning of the steppedpiston 75 affords a means of controlling the variations of the finalcompression in the diesel cylinder 11. The stabilizer 63 has the usualadjustable wheel 94 which raises the final compression pressure in thediesel cylinder so that the engine can be started when cold. The wheel94 acts on a spring 95 which in turn acts on the differential piston 75so that the final compression pressure may be raised during engine warmup.

When the turbine 42 operates in a zone extending from medium load tomaximum load, regulation of the power plant can be afforded exclusivelyby direct control of the fuel rack 41 from the governor 45, for thegasifier delivery can be adapted to the receiver machine requirements inthis range by varying the length of stroke of the free pistonassemblies. With the arrangement thus far described and without benefitof the subject invention, it is not possible to further vary the lengthof stroke of the free piston assemblies to reduce the gasifier deliveryfor idle and low load conditions. Under these conditions the gasifierdelivery pressure need only be in the neighborhood of one atmosphere. Inthis load region the minimum delivery from the gasifier is set by theminimum outer dead points of the free piston assemblies which aredetermined by the position of the diesel intake and exhaust ports 12 and13. The minimum outer dead points of the free pistons occur when theports 12 and 13 are opened by the pistons in an amount just enough tosupply and scavenge the diesel cylinder. The gasifier delivery at suchtime is greater than the turbine can accommodate at low and idle loadsif the main intake and exhaust ports 12 and 13 are located for maximumefliciency at medium and full operating loads.

Heretofore, after shortening the piston stroke as much as possible, ithas been common to allow the surplus gasifier exhaust to escape toatmosphere at low loads and idle by way of a blow off valve located inthe exhaust conduit 43 and ahead of the turbine inlet. It is apparentthat such blow off represents an efiiciency loss at low load and idleconditions which should be obviated.

In order to reduce the losses resulting from gas escaping during theidle running and low loads, the invention provides a means for reducingthe piston stroke at such conditions. The diesel cylinder 11 is providedwith a set of auxiliary intake and exhaust ports 73 and 79 which arelocated inboard of the main ports 12 and 13. A pair of ring valves 80and 81 are rotatably mounted on the diesel cylinder 11 and are providedwith ports 82 and 83 which can be brought into and out of registry withthe ports 73 and 79, as may be seen in FIGURES 2 and 3. The auxiliaryintake and exhaust ports 78 and 79 are closed by the ring valves 80 and81 when the turbine is at medium or high load condition and are openedduring idle or low load condition. The opening and closing of theauxiliary intake and exhaust ports is accomplished automatically by gearracks 84 and 85 which engage gear teeth 86 and 87 formed on theperiphery of the ring valves 80 and 81. The gear racks 84 and 85 connectto pistons 88 and 89 in cylinders 90 and 91 which communicate with thefluid pressure of the governor 45. As the turbine load decreases to lowload and idle condition, the governor control pressure decreases and thesprings 92 and 93 act on the pistons 88 and 89 against the reducedpressure to open the auxiliary ports 78 and 79. The control pressurerises at high loads and moves the ring valves $0 and 81 to closedposition.

The auxiliary ports 78 and 79 afford a means for reducing the pistonstroke at low load conditions and thus the gasifier delivery so that thegasifier blow off is not required. The piston stroke is shortened as thepistons need only move outward sufficiently to register with theauxiliary ports. The invention thus provides reduced outer dead pointsfor the piston assemblies at low or idle load condition.

We claim:

1. An internal combustion free piston power plant comprising a dieselcylinder having main intake and exhaust ports and auxiliary intake andexhaust ports spaced therefrom, a compressor cylinder, a cushioncylinder, a piston assembly reciprocal in said cylinders and having avariable stroke, a scavenge chamber arranged to receive compressed airfrom said compressor cylinder and to feed said air to said dieselcylinder through said intake ports, fuel injection means for said dieselcylinder, a receiver machine subject to variable loads and arranged toreceive exhaust gas from said diesel cylinder through said exhaustports, separate intake and exhaust valves for clos ing said auxiliaryintake and exhaust ports at high load conditions of said receivermachine and for opening said auxiliary ports at low load conditions, andgovernor means responsive to said various load conditions forautomatically operating said valves for said auxiliary ports, said portsbeing so located that the piston assembly uncovers the auxiliary portsprior to the main ports on the power stroke to reduce pistondisplacement and exhaust gas delivery at low load conditions.

2. Apparatus in accordance with claim 1 wherein said intake and exhaustvalves each comprises a ring movably mounted on the outer periphery ofthe diesel cylinder and having ports therethrough adapted to be broughtinto and out of registry with the respective auxiliary intake andexhaust ports of said diesel cylinder on movement of said ring.

References Cited in the file of this patent UNITED STATES PATENTSTsuneda Aug. 7, 1938 Morain Feb. 3, 1948 Bachle et a1 Sept. 30, 1958Huber Mar. 31, 1959

